This invention relates to a magnetic tape backing leaf spring, or shoe, assembly providing back support for a running magnetic tape, in particular of the type contained in "cassette" housings and the like recording devices, for the purpose of elastically biasing a running magnetic tape to contact a magnetic head in a tape recorder/player or the like apparatus.
As is known, currently available playing cassettes or recording cassettes are provided, for biasing the tape to contact a playing or recording magnetic head as well as for maintaining that contact relationship, with an elastic leaf spring comprising a metal reed which carries a felt pad or the like adhesively secured to the central portion thereof. This felt pad is selected for direct contact with the magnetic tape by virtue of its low frictional resistance, the elastic metal reed taking up the pressure applied by the magnetic head to the tape and ensuring continued contact of the latter without excessive drag.
A tape backing leaf spring assembly so constructed is quite satisfactory as far as its action on the magnetic tape is concerned, but has serious disadvantages from the standpoint of the operational reliability. Owing to the friction set up by the tape running past the felt pad--quite appreciable, albeit somewhat reduced--it may happen after a number of hours of operation that the felt pad separates from, or is dislodged along the metal reed, thus nullifying the action expected from the leaf spring. In such conditions, the contact between the magnetic tape and magnetic head becomes questionable, and the replacement of the leaf spring assembly requires that the cassette housing be opened up, an operation which is not usually within the capabilities of a normal user.
Thus, the separation and dislodging of the felt pad from the reed of the leaf spring represent a serious drawback which may effect the useability of the cassette as a whole, nor can any of the adhesives currently used for retaining the felt pad position obviate it, when the apparatus is utilized in a hot and damp climate.
Thus, the need is felt for different solutions to the problem of securing the felt pad to the metal reed, which solutions should not contemplate the use of adhesives, or only utilize them for seconding purposes. Accordingly, leaf springs have been proposed which have retention lips at their middle portions tailored to the size of the felt pad and defining a substantially box-like sectional profile at least partially embracing said felt pad. In particular, the box-like sectional profile engages the pad corners.
That approach is quite effective to prevent definitively the felt pad from coming loose, but has the very serious disadvantage of raising the manufacturing costs considerably, and above all of preventing the adoption of continuous manufacturing methods for the leaf springs on automatic equipment. In fact, conventional leaf springs with adhesively attached felt pads are obtained by combining a continuous band consisting of a row of abutting reeds with a further continuous band formed by the stock material wherefrom the felt pads originate, which is glued continuously to the former. The two-band combination is then cut to produce individual leaf spring blanks. On the contrary the leaf springs comprising a reed which clads the felt pads box-like have to be individually finished and the single felt pads have to be inserted into the respective seats. Accordingly the box-encased felt pad leaf springs are only employed in magnetic tape cassettes of higher quality that may warrant the increased cost. However, for the great majority of the tape cassettes available commercially, the situation is still unchanged, i.e. leaf springs with glued-on felt pads are used which are quick and economical to manufacture but unsatisfactory as regards the reliability.